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Fact Sheet

Gaia is an ambitious mission to chart a three-dimensional map of our Galaxy, the Milky Way, in the process revealing the composition, formation and evolution of the Galaxy. Gaia will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group. This amounts to about 1 per cent of the Galactic stellar population.

Mission Objectives

Gaia was adopted within the scientific programme of the European Space Agency (ESA) in October 2000. The mission aims to:

measure the positions of ~1 billion stars both in our Galaxy and other members of the Local Group, with an accuracy down to 20 μas

perform spectral and photometric measurements of all objects

derive space velocities of the Galaxy's constituent stars using the stellar distances and motions

create a three-dimensional structural map of the Galaxy

The gathered large datasets will provide astronomers with a wealth of information covering a wide range of research fields: from solar system studies, galactic astronomy, cosmology to general relativity.

Mission Name

Gaia originally stood for Global Astrometric Interferometer for Astrophysics. As the project evolved, the single interferometer concept was replaced by a new payload design. The mission name remained, however, even though it no longer reflects the methods used to perform the science operations.

Spacecraft

The Gaia spacecraft consists of three major functional modules: the payload module, the mechanical service module and the electrical service module. It carries a single integrated instrument that comprises three major functions: astrometry, photometry and spectrometry. The three functions use two common telescopes and a shared focal plane, with each function having a dedicated area on the large 0.5m × 1m CCD detector array.

Instruments

The payload consists of a single integrated instrument the design of which is characterised by:

A dual telescope concept, with a common structure and a common focal plane. Both telescopes are based on a three-mirror anastigmat (TMA) design. Beam combination is achieved in image space with a small beam combiner.

Silicon-carbide (SiC) ultra-stable material is used for mirrors and telescope structure

A highly robust measurement system for the Basic Angle between the two telescopes' pointing directions

A large common focal plane with an array of 106 CCDs. The large focal plane also includes areas dedicated to the spacecraft's metrology and alingment measurements

Three instrument functions:

Astrometry

accurate measurements, even in densely populated sky regions of up to 3 million stars/deg²

Photometry

continuous spectra in the band 320-1000 nm for astrophysics and chromaticity calibration of the astrometry

Spetrometry

high resolution, grating, narrow band: 847-874 nm

Orbit

Gaia will operate in a Lissajous-type orbit, around the L2 point of the Sun-Earth system, which is located 1.5 million km from the Earth in the anti-Sun direction. The orbit is not impacted by Earth eclipses. The orbit period is about 180 days and the size of the orbit is typically 340 000 × 90 000 km. An operational lifetime of 5 years is planned.

Operations Centre

The Gaia spacecraft will be controlled from the European Space Operations Centre (ESOC, Darmstadt, Germany) using the two ground stations Cebreros (Spain) and Perth (Australia).